linux-kernel - Re: [RFC][PATCH 1/2] x86: Allow breakpoints to emulate call functions

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAHk-=wiwc8NDahj455iBWmYyvDDS+sN1TObFsxxS51gNbtZ9iw@mail.gmail.com>
Date:   Sat, 4 May 2019 13:28:00 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andy Lutomirski <luto@...nel.org>,
        Nicolai Stange <nstange@...e.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Jiri Kosina <jikos@...nel.org>,
        Miroslav Benes <mbenes@...e.cz>,
        Petr Mladek <pmladek@...e.com>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        Shuah Khan <shuah@...nel.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Mimi Zohar <zohar@...ux.ibm.com>,
        Juergen Gross <jgross@...e.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nayna Jain <nayna@...ux.ibm.com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Joerg Roedel <jroedel@...e.de>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>, stable <stable@...r.kernel.org>
Subject: Re: [RFC][PATCH 1/2] x86: Allow breakpoints to emulate call functions

On Sat, May 4, 2019 at 1:12 PM Andy Lutomirski <luto@...capital.net> wrote:
>
> As an aside, is it even *possible* to get #BP from v8086 mode?  On a quick SDM read, the INT3 instruction causes #GP if VM=1 and IOPL<3.  And, if we allow vm86() to have IOPL=3, we should just remove that ability. It’s nuts.

We've definitely historically allowed IOPL=3 with the whole "iopl()"
system call. And yes, afaik it works together with the vm86 system
call too. I think we copy the unsafe bits from the original eflags, so
if you do iopl(3) followed by vm86(), you will be running in vm86 mode
with iopl 3.

> (We should maybe consider a config option for iopl() that defaults off. We’ve supported ioperm() for a long, long time.)

It's entirely possible that nobody uses iopl() and we should make it a
config option that defaults to off.

But we've already done that with the VM86 support entirely, and I'm
not sure modern distros even enable it.

And obviously vm86 mode isn't available at all with a 64-bit kernel,
so this is all slowly becoming more or less moot.

                  Linus